Dutch astronaut André Kuipers of the European Space Agency was also onboard after more than a week performing scientific experiments aboard the station.

The Soyuz craft landed with the aid of rockets and a series of parachutes near the northern town of Arkalyk.

Officials had expressed concern about a persistent helium leak discovered months ago in the Soyuz 7 capsule while it was docked to the station.

Helium is used to pressurize the Soyuz craft's fuel tanks prior to its return to Earth. It prompted discussions between NASA and the Russian space agency, but administrators agreed it posed no risk to either the spacecraft or the crew.

A team of 160 people along with eight helicopters, all-terrain vehicles and aircraft were deployed to ensure the safe recovery of the crew.

In May 2003, the first Soyuz capsule to carry an American astronaut back from orbit went seriously off course during a "ballistic" descent that put it 275 miles from its intended landing zone. The steep re-entry was blamed on a malfunctioning guidance system.

The problem was fixed and the next mission in October 2003 occurred without mishap.

The returning crew, known as Expedition 8, arrived at the space station in October 2003 aboard Soyuz 7.

It conducted a battery of experiments ranging from cellular biology to autonomous satellite technology.

One experiment studied three-dimensional tissue growth to examine how tissue retains its form and function. NASA said the experiment has applications against AIDS, heart disease and cancer.

The crew also tended to a greenhouse in the station growing vegetables and other plants considered crucial for long duration spaceflights.

Much of that work will aid preparations for the upcoming manned Mars mission called for in the White House's Vision for Space Exploration.

The Soyuz craft is now the only vehicle servicing the $95 billion station after the shuttle Columbia broke up on re-entry in February 2003.

Soyuz's return to Earth marks its ninth trip to the orbiting outpost. The vehicle is replaced after each flight and serves as the crew's lifeboat in an emergency.

Russian supply ships, known as Progress capsules, also make regular visits to the station carrying food, water and experiments.

The shuttle is not scheduled to fly again until March 2005. Two flights are already dedicated to finishing the station, but not ferrying a space station crew, NASA said.

The Soyuz capsules are expected to continue rotating crews at six-month intervals.

The incoming Expedition 9 crew, consisting of astronaut Mike Fincke and cosmonaut Gennady Padalka, assumed control of the space station when the hatch closed to the Soyuz carrying the outgoing crew home.